The Patent of United States published under reference US 2001/0040735A1 describes a variable-focus lens. The variable-focus lens is constructed by making small changes in the equatorial diameter of an elastically deformable lens. The lens may be deformed by radial tension exerted in a plane generally perpendicular to the optical axis. The radial tension may be exerted by mechanical means or by rings embedded in or attached to the equator of the lens, whose diameter can be altered by heating or by the application of an electric or magnetic field.
The technique described in the prior art document not only implies the use of complicated and numerous actuators for changing the focus of the lens, but it is also difficult to implement in small devices or apparatus.